Well I really do not want to get into the argument about HTML structure (suffice to say John is completely right), but until someone can show any merit or any benefit at all in having H1 tags, this is not something we'd offer.

Why would we start complicating the product with some technical gubbins that few people will understand, especially when it has no actual benefit?

I agree that it would be nice to have more powerful text Style control in Xtreme and Web Designer, but that's really a completely separate issue, and one day we'll add it.